Accelerating filtration by introducing an oscillation paradigm and its atomistic origin

Abstract

Developing high efficiency and anti-fouling filtration technologies is critical to meet the global water crisis. Improving the filtration efficiency while maintaining selectivity and reducing membrane contamination is a huge challenge. To overcome this challenge, we introduced an oscillation paradigm into filter membranes and discovered a previously unknown mechanism by molecular dynamics simulations. An ultrahigh permeability 355.04 L per cm² per day per MPa is achieved and the salt rejection rate can be maintained at almost 99%, when using a designed covalent organic framework membrane (Hex-Aza-COF-2) in our simulations. A new concept of “spatial permeability” is proposed, which attributes the ultrahigh permeability to the loss of hydrogen bonds at the liquid/membrane interface caused by the oscillation, resulting in a larger effective pore for water molecule transport and a shorter residence time of water molecules in the membrane. The newly proposed oscillation filtration paradigm breaks the permeability-selectivity trade-off rule, overcomes the drawbacks of low permeability of traditional selectivity membranes, and proposes a new theory for designing high-performance filtration membranes.